The Human Urinary System

After your cells convert complex carbohydrates into usable forms of energy, waste products must be removed.

Excretion: the removal of waste products from cells.

There are five important excretory organs in humans:

Skin: excretes sweat, containing water, ions and urea Lungs: excrete carbon dioxide and water Liver: excretes bile, containing bile pigments,

cholesterol and mineral ions Gut(large intestine): excretes mucosa cells, water and

bile in feces. (The bulk of feces comprises plant fibre and bacterial cells, which have never been absorbed into the body, so are not excreted but egested.)

Kidneys: excrete urine, containing urea, mineral ions, water and other "foreign" chemicals from the blood.

This section is mainly concerned with the excretion of nitrogenous waste as urea. The body cannot store protein in the way it can store carbohydrate and fat, so it cannot keep excess amino acids. The "carbon skeleton" of the amino acids can be used in respiration, but the nitrogenous amino group must be excreted.

Amino Acid Metabolism

Amino acid metabolism takes place in the liver, this involves two main stages:

1. Deamination

2. Urea Synthesis

1. Deamination An amino group is removed

from an amino acid to form ammonia and an organic acid.

catalyzed by the enzyme glutamate dehydrogenase.

The NADH produced is used in the respiratory chain;

the a-ketoglutarate enters the Krebs cycle;

and the ammonia is converted to urea in the urea cycle.

2. Urea Synthesis Ammonia is converted to urea, ready for excretion by the kidney.

Ammonia is highly toxic. Urea is less toxic than ammonia, so it is safer to have in the bloodstream.

"costs" 3 ATP molecules to make one urea molecule.

Uric acid: waste product formed also by breaking down nucleic acids

The Urinary System

The Urinary System is composed of the following:

1. Renal Arteries: Carries blood to the kidneys

Renal Veins: Carry blood away from the kidney

2. Kidneys: Wastes are removed from

the blood and sent to the bladder through the Ureter

Helps maintain water balance

Humans cannot survive more than a couple of days without water

Humans deplete water reserve faster than food reserve (10 % loss of water = death)

3. Bladder: Stores urine until it

reaches a specific volume where receptors will send signals to the brain.

If the volume of urine surpasses a particular threshold, voluntary control is lost and the urine is excreted.

4. Urethra: - Urine is excreted from the body via the Urethra.

Male: Urethra is located through the penis

Female: Urethra located ventral to (above) the vagina

The KidneyThere are 3 regions of the

kidney:1. Cortex: (5) granulated

layer that dips down between the Medulla

2. Medulla: (4) striated or lined layer.

contains conical masses of tissue called Renal Pyramids.

These are lined with tubes that join with others (3) to form the Renal Pelvis

3. Renal Pelvis: (14) Inner space that leads into the ureter (15)

Nephron

Kidney is composed of over 1 million nephrons

Afferent arterioles (branches from the renal artery) supply the nephron with blood and branch into a capillary bed called the Glomerulus.

The Glomerulus then branches out into more arterioles called the Efferent arterioles. These lead the blood out and into another set of capillaries called the Peritubular Capillaries

Peritubular Capillaries: These capillaries wrap around the kidney tubule

Bowman’s Capsule: Cuplike structure that surrounds the glomerulus.

Outer layer: epithelial cells

Inner layer: specialized cells that allow easy passage of molecules.

The bowman’s capsule, afferent and efferent arterioles are located in the cortex of the kidney.

Fluids or products that will be used to form urine, are emptied into the bowman’s capsule from the blood.

Bowmans capsule narrows into the proximal tubule. This carries urine into the Loop of Henle to the distal tubule and collects in the Collecting ducts.

The Loop of Henle and collecting ducts lie within the triangular-shaped pyramids of the medulla.